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1 for more information www.linear.com/LT8619 typical application features description 60v, 1.2a synchronous monolithic buck regulator with 6a quiescent current the lt ? 8619 is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 6a of quiescent current. the LT8619 can deliver 1.2a of continuous current. top and bottom power switches are included with all necessary circuitry to minimize the need for external components. low ripple burst mode ? operation enables high efficiency down to very low output currents while keeping the output ripple to 10mv p-p . a sync pin allows forced continuous mode operation synchronized to an external clock. internal com - pensation with peak current mode topology allows the use of small inductors and results in fast transient response and good loop stability. the en/uv pin has an accurate 1v threshold and can be used to program v in undervoltage lockout or to shut down the LT8619, reducing the input supply current to below 0.6a . the pg flag signals when v out is within 7.5% of the programmed output voltage. the LT8619 is available in a small 16- lead msop and 10-lead 3mm 3mm dfn packages with exposed pad for low thermal resistance. applications n wide input voltage range: 3v to 60v n fast minimum switch-on time: 30ns n ultralow quiescent current burst mode operation: n 6a i q regulating 12v in to 3.3v out n 10mv p-p output ripple at no load n synchronizable/programmable fixed frequency forced continuous mode operation: 300khz to?2.2mhz n high efficiency synchronous operation: n 92% efficiency at 0.5a, 5v out from 12v in n 90% efficiency at 0.5a, 3.3v out from 12v in n low dropout: 360mv at 0.5a n low emi n accurate 1v enable pin threshold n internal soft-start and compensation n power good flag n small thermally enhanced 16-lead msop package and 10-lead (3mm 3mm) dfn packages n 12v automotive systems n 12v and 24v commercial vehicles n 48v electric and hybrid vehicles n industrial supplies all registered trademarks and trademarks are the property of their respective owners. efficiency at v out = 5v 5v, 1.2a step-down converter 8619 1 66 1 8619 1 1 6 6 1 f 1 1 16 LT8619/LT8619-5 8619f f v in v in v in load current (ma) 0.001 0.01 0.1 1 10 l = 10h, ihlp-2020bz-01 100 1k 10k 0 10 20 30 40 50 60 = 48v 70 80 90 100 0.0001 0.001 0.01 efficiency (%) power loss (w) 8619 ta01b = 24v 0.1 1 10 ef?ciency at v out = 5v power loss = 12v osc = 700khz burst mode operation efficiency
2 for more information www.linear.com/LT8619 absolute maximum ratings v in , en/uv ................................................................ 60v bi as .......................................................................... 30v bs t pin above sw pin................................................ 4v pg, sync, out. .......................................................... 6v fb ............................................................................... 2v (notes 1, 2) order information lead free finish tape and reel part marking* package description temperature range LT8619edd#pbf LT8619edd#trpbf lgnp 10-lead (3mm 3mm) plastic dfn C40c to 125c LT8619idd#pbf LT8619idd#trpbf lgnp 10-lead (3mm 3mm) plastic dfn C40c to 125c LT8619emse#pbf LT8619emse#trpbf 8619 16-lead plastic msop C40c to 125c LT8619imse#pbf LT8619imse#trpbf 8619 16-lead plastic msop C40c to 125c LT8619emse-5#pbf LT8619emse-5#trpbf 86195 16-lead plastic msop C40c to 125c LT8619imse-5#pbf LT8619imse-5#trpbf 86195 16-lead plastic msop C40c to 125c consult adi marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a la bel on the shipping container. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. some packages are available in 500 unit reels through designated sales channels with #trmpbf suffix. http://www.linear.com/product/LT8619#orderinfo 11 1 1 9 6 8 1 ja = 43c/w, jc = 10c/w exposed pad (pin 11) is gnd, must be soldered to pcb 1 2 3 4 5 6 7 8 nc v in nc en/uv rt pg sync gnd 16 15 14 13 12 11 10 9 sw sw bst nc intv cc bias fb/out* fb/out* top view 17 gnd mse package 16-lead plastic msop ja = 40c/w, jc = 10c/w exposed pad (pin 17) is gnd, must be soldered to pcb *fb for LT8619, out for LT8619-5 pin configuration operating junction temperature (note 3) lt861 9 e, LT8619 e-5 .......................... C 40 c to 12 5 c lt861 9 i, LT8619 i-5 ............................ C 40 c to 12 5 c storage temperature range .................. C 65 c to 150 c LT8619/LT8619-5 8619f
3 for more information www.linear.com/LT8619 the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v en/uv = 2v unless otherwise noted (notes 2, 3) electrical characteristics parameter conditions min typ max units switching loop v in minimum input voltage 3.0 v v in quiescent current at no load v in = 12v, v en/uv = 0v l 0.6 0.6 1.0 3.0 a a v in = 12v, v out = 3.3v, r t = 66.5k, v en/uv = 2v, v sync = 0v l 6 6 10 18 a a v in = 12v, v out = 3.3v, r t = 66.5k, v en/uv = 2v, floats sync 10 a v in = 12v, v out = 3.3v, r t = 66.5k, v en/uv = 2v, v sync = intv cc 3 ma v in current in regulation v in = 12v, v out = 3.3v, r t = 66.5k, v en/uv = 2v, v sync = 0v i load = 100a i load = 1ma l l 38 320 65 400 a a bias pin current consumption v in = 12v, v bias = 3.3v, i load = 0.5a, f osc = 700khz 2.2 ma regulated output voltage LT8619-5, v in = 12v, v sync = intv cc , no load l 4.975 4.925 5.0 5.0 5.025 5.075 v feedback voltage LT8619, v in = 12v, v sync = intv cc , no load l 0.796 0.788 0.8 0.8 0.804 0.812 v v feedback voltage line regulation v in = 4v to 50v, v sync = intv cc l 0.004 0.03 %/v feedback pin input current LT8619, v fb = 0.8v 20 na minimum on-time LT8619, i load = 0.5a, v sync = intv cc l 30 60 ns minimum off-time 100 150 180 ns top switch peak current limit l 1.5 1.75 2.0 a bottom switch current limit 1.8 a bottom switch reverse current limit v sync = intv cc 0.55 a soft-start duration v in = 12v, v out = 3.3v, no load, c out = 22f 0.2 ms en/uv to pg high delay c intvcc = 1f, v out = 3.3v, no load, c out = 22f 0.66 ms en/uv to pg low delay 10 s oscillator and sync operating frequency r t = 162k l 260 300 340 khz r t = 66.5k l 630 700 770 khz r t = 20k l 1.9 2.0 2.1 mhz synchronization frequency f sync f osc l 0.3 2.2 mhz sync threshold frequency synchronization burst mode operation floats sync pin, pulse-skipping mode forced continuous mode 0.35 1.6 1 0.6 1.2 2.0 0.95 2.4 v v v b sync pin current built-in sourcing current, v sync = 0v built-in sinking current, v sync = 3.3v C0.2 3.0 a a LT8619/LT8619-5 8619f
4 for more information www.linear.com/LT8619 electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v en/uv = 2v unless otherwise noted (notes 2, 3) note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: all currents into device pins are positive; all currents out of device pins are negative. all voltages are referenced to ground unless otherwise specified. note 3: the LT8619 is tested under pulse load conditions such that t j ? t a . the LT8619e is guaranteed to meet performance specifications from 0c to 125c junction temperature. specifications over the C40c to 125c operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. the LT8619i is guaranteed over the full C40c to 125c operating junction temperature range. high junction temperatures degrade operating lifetimes. operating lifetime is derated at junction temperatures greater than 125c. note 4: this ic includes overtemperature protection that is intended to protect the device during overload conditions. junction temperature will exceed 150c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature will reduce lifetime. parameter conditions min typ max units switch, logic and power good top switch on-resistance i load = 0.1a 0.45 ? bottom switch on-resistance i load = 0.1a 0.22 ? en/uv power-on threshold en/uv rising l 0.94 1.0 1.1 v en/uv power-on hysteresis 40 mv en/uv shutdown threshold en/uv falling l 0.34 0.56 0.92 v en/uv pin current v en/uv = 2v C100 100 na overvoltage threshold v fb rising wrt. regulated v fb 3.75 % positive power good threshold v fb rising wrt. regulated v fb l 5 7.5 10 % negative power good threshold v fb falling wrt. regulated v fb l C5 C7.5 C10 % positive power good delay v fb = 0.8v 0.9v to pg low v fb = 0.9v 0.8v to pg high 60 35 s s negative power good delay v fb = 0.8v 0.7v to pg low v fb = 0.7v 0.8v to pg high 60 35 s s pg leakage v pg = 3.3v, power good 100 na pg v ol i pg = 100a l 0.01 0.3 v LT8619/LT8619-5 8619f
5 for more information www.linear.com/LT8619 typical performance characteristics 2mhz efficiency at v out = 3.3v efficiency at v out = 5v efficiency at v out = 3.3v efficiency vs v in no load i vin at 700khz no load i vin vs temperature 700khz efficiency at v out = 5v 2mhz efficiency at v out = 5v 700khz efficiency at v out = 3.3v LT8619/LT8619-5 8619f 10k 80 85 90 95 100 efficiency (%) ef?ciency vs v in 8619 g07 v out = 3.3v f sw = 700khz 0 forced continuous mode l = 10h ihlp-2020bz-01 0.5a load 1.2a load temperature (c) ?50 ?25 0 25 50 10 75 100 125 150 0.5 1 10 20 i vin (a) vin 20 8619 g09 f osc = 700khz burst mode operation shutdown 12v 12v 60v 60v v in (v) 1 30 10 100 0.1 1 10 100 1k 10k i vin (a) no load i vin at 700khz 40 8619 g08 forced continuous mode burst mode operation 3.3v 5v 3.3v 3.3v v out : pulse- skipping mode shutdown 50 f osc = 700khz no load load current (ma) 0.001 0.01 0.1 1 10 100 1k 60 10k 0 10 20 30 40 50 60 70 80 70 90 100 efficiency (%) 700khz ef?ciency at v out = 5v 8619 g01 v in = 12v f osc = 700khz forced continuous mode pulse- skipping mode burst mode operation 80 l = 10h ihlp-2020bz-01 load current (ma) 0.001 0.01 0.1 1 10 100 1k load current (ma) 90 10k 0 10 20 30 40 50 60 70 80 100 90 100 efficiency (%) 700khz ef?ciency at v out = 3.3v 8619 g02 v in = 12v f osc = 700khz forced continuous mode pulse- skipping mode burst mode operation efficiency (%) l = 10h ihlp-2020bz-01 load current (ma) 0.001 0.01 0.1 1 10 100 1k 2mhz ef?ciency at v out = 3.3v 10k 0 10 20 30 40 50 60 70 80 8619 g04 90 100 efficiency (%) 2mhz ef?ciency at v out = 5v 8619 g03 v in = 12v f osc = 2mhz forced continuous mode pulse- skipping mode burst mode operation v in = 12v l = 4.7h ihlp-2020ab-01 f osc = 2mhz forced continuous mode pulse- skipping mode burst mode operation 0.001 l = 3.3h ihlp-2020ab-01 load current (a) 0 0.2 0.4 0.6 0.8 1.0 1.2 0.01 70 75 80 85 90 95 100 efficiency (%) ef?ciency at v out = 5v 8619 g05 0.1 forced continuous mode burst mode operation l = 10h, ihlp-2020bz-01 f osc = 700khz 48v 24v 12v load current (ma) 0.001 0.01 1 0.1 1 10 100 1k 10k 0 10 20 30 10 40 50 60 70 80 90 100 efficiency (%) out 8619 g06 100 burst mode operation = 700khz osc f v in = 48v in = 24v v in = 12v l = 10h, ihlp-2020bz-01 v 1k v in (v) 0 10 20 30 40 50 60 70 75
6 for more information www.linear.com/LT8619 typical performance characteristics en/uv threshold top fet current limit vs duty cycle switch resistance dropout v out = 3.3v load regulation line regulation dropout vs temperature f sw LT8619/LT8619-5 8619f 25 1.9 2.0 current limit (a) 8619 g14 v in = 12v v out = 3.3v load current = 100ma top switch temperature (c) ?50 50 ?25 0 25 50 75 100 125 150 0 100 75 200 300 400 500 600 700 800 900 1000 r ds(on) (m) 100 switch resistance 8619 g15 bottom switch v out = 3.3v ?v out = ?1% f sw = 2mhz l = 3.3h, ihlp-2020ab-01 forced continuous mode load current (a) 0 125 0.2 0.4 0.6 0.8 1.0 1.2 0 0.2 0.4 0.6 150 0.8 1.0 dropout voltage (v) 8619 g16 v in = 12v v out = 3.3v, no load forced continuous mode f sw = 700khz temperature (c) ?50 ?1.00 ?25 0 25 50 75 100 125 150 ?5 ?4 ?0.75 ?3 ?2 ?1 0 1 2 3 4 5 ?f sw (%) ?0.50 sw 8619 g18 f sw = 2mhz 1.2a load no load 1.0a load 0.5a load temperature (c) ?50 ?25 ?0.25 0 25 50 75 100 125 150 0 0.25 0.50 v in = 12v 0 0.75 1.00 1.25 1.50 1.75 2.00 dropout voltage (v) 8619 g17 v out = 3.3v, ?v out = ?1% f osc = 700khz 0.25 forced continuous mode (continuous operation above max junction temperature may permanently damage the device) l = 10h, ihlp-2020bz-01 0.50 0.75 1.00 ?v out (%) out 8619 g10 v in = 12v v out = 3.3v f osc = 700khz f sw = 700khz forced continuous mode load current (a) 0 0.2 0.4 0.6 0.8 1.0 1.2 no load ?0.2 ?0.1 0 0.1 0.2 ?v out (%) load regulation 8619 g11 v out = 2.4v, no load f sw = 400khz forced continuous mode forced continuous mode v in (v) 1 10 100 ?0.10 ?0.05 0 0.05 0.10 temperature (c) ?v out (%) 8619 g12 shutdown threshold power?on threshold en/uv rising en/uv falling temperature (c) ?50 ?25 0 ?50 25 50 75 100 125 150 0 0.2 0.4 0.6 ?25 0.8 1.0 1.2 v en/uv (v) en/uv threshold 8619 g13 f sw = 700khz l = 10h ihlp-2020bz-01 duty cycle (%) 0 0 20 40 60 80 100 1.5 1.6 1.7 1.8
7 for more information www.linear.com/LT8619 typical performance characteristics minimum off-time power good, overvoltage threshold power good delay v in uvlo i bias vs load minimum on-time i bias vs f sw i bias at 700khz vs temperature i bias at 2mhz vs temperature LT8619/LT8619-5 8619f 25 125 150 2.5 2.6 2.7 2.8 2.9 3.0 v in uvlo (v) in 50 8619 g23 v in rising v in = 12v v out = 3.3v forced continuous mode f sw = 2mhz f sw = 700khz load current (a) 0 0.2 75 0.4 0.6 0.8 1.0 1.2 0 2 4 6 8 100 10 12 i bias (ma) bias 8619 g24 1.2a load 1a load no load temperature (c) ?50 125 ?25 0 25 50 75 100 125 150 0 2 150 4 6 8 10 i bias (ma) bias 8619 g26 v in = 12v v out = 3.3v forced continuous mode (continuous operation above max junction temperature may permanently damage the device) 0 bias = v out 0.5a load temperature (c) ?50 ?25 0 25 50 75 100 20 125 150 0 4 8 12 16 20 24 i bias (ma) 40 1.2a load 1a load 0.5a load no load i bias at 2mhz vs temperature 8619 g27 v in = 12v v out = 5v forced continuous mode (continuous operation above max junction temperature may permanently damage the device) bias = v out 60 0.2 0.6 1.0 1.4 1.8 2.2 0 2 4 6 v out = 3.3v 80 8 10 v in = 12v v out = 3.3v l = 10h forced continuous mode 1a load no load f sw (mhz) i bias (ma) 100 8619 g25 120 minimum on-time (ns) minimum on time 8619 g19 0.5a load no load no load temperature (c) f sw = 2mhz ?50 ?25 0 25 50 75 100 125 150 140 forced continuous mode 150 160 170 180 minimum off time (ns) 8619 g20 0.5a load temperature (c) ?50 ?25 0.2a load 0 25 50 75 100 125 150 ?10.0 ?7.5 ?5.0 temperature (c) ?2.5 0 2.5 5.0 7.5 10.0 power good, overvoltage threshold (%) power good, overvoltage threshold 8619 g21 ov ?50 ppg v fb rising ppg v fb falling npg v fb rising npg v fb falling v fb ? v pgth (mv) 0 20 40 60 80 ?25 100 0 25 50 75 100 power good delay (s) 8619 g22 v out = 1.6v, no load f sw = 700khz 0 forced continuous mode v in falling temperature (c) ?50 ?25 0 25 50 75 100
8 for more information www.linear.com/LT8619 typical performance characteristics forced continuous mode no load switching waveform forced continuous mode switching waveform at minimum on-time forced continuous mode transient load step from 10ma to 1a pulse-skipping mode transient load step from 10ma to 1a bust mode transient load step from 10ma to 1a forced continuous mode frequency synchronization 200ns/div v out (ac) 2mv/div i l 200ma/div sw 10v/div 8619 g28 v in = 12v, v out = 3.3v f sw = 2mhz, l = 3.3h, c out = 22f top = 200ns/div, bot = 5ns/div, persistence mode i l 200ma/div sw 20v/div sw (zoom in) 10v/div 8619 g29 v in = 53.7v, v out = 3.3v, 0.5a load f sw = 2mhz, l = 3.3h, c out = 22f 20s/div v out 200mv/div i load 1a/div sw 10v/div 8619 g30 v in = 12v, v out = 3.3v f osc = 2mhz, l = 3.3h, c out = 22f 20s/div 8619 g31 v out 200mv/div i load 1a/div sw 10v/div v in = 12v, v out = 3.3v f osc = 2mhz, l = 3.3h, c out = 22f 20s/div 8619 g32 v out 200mv/div i load 1a/div sw 10v/div v in = 12v, v out = 3.3v f osc = 2mhz, l = 3.3h, c out = 22f v out (ac) 20mv/div sync 2v/div sw 10v/div sw (zoom in) 10v/div sync (zoom in) 2v/div 8619 g33 v out (ac, zoom in) 20mv/div top = 10s/div, bot = 200ns/div v in = 12v, v out = 3.3v, no load f osc = 700khz, l = 10h, c out = 22f f sw (free running) = 700khz, f sync = 1.2mhz LT8619/LT8619-5 8619f
9 for more information www.linear.com/LT8619 typical performance characteristics en/uv shut down v out = 2.4v start-up dropout performance v out = 5v start-up dropout performance en/uv start-up 1s/div v out 1v/div v in 1v/div pg 2v/div sw 5v/div 8619 g34 v in v out v out = 2.4v, 10 load f sw = 400khz, l = 15h, c out = 47f pg 100k pull-up by intv cc forced continuous mode 8619 g35 1s/div v out 1v/div v in 1v/div pg 2v/div sw 5v/div v in v out v out = 5v, 10 load f sw = 700khz, l = 10h, c out = 22f pg 100k pull-up by intv cc forced continuous mode 8619 g36 100s/div v out 1v/div en/uv 2v/div pg 2v/div sw 10v/div v in = 12v, v out = 3.3v, no load f osc = 2mhz, l = 3.3h, c out = 22f forced continuous mode 8619 g37 2s/div v out 1v/div en/uv 2v/div pg 2v/div sw 10v/div v in = 12v, v out = 3.3v, no load f osc = 2mhz, l = 3.3h, c out = 22f forced continuous mode LT8619/LT8619-5 8619f
10 for more information www.linear.com/LT8619 pin functions nc (pin 1, 3, 13, msop only): no connect. these pins are not connected to the internal circuitry. v in (pin 1/pin 2) : the v in pin supplies current to the LT8619 internal circuitry and to the internal topside power switch. be sure to place the positive terminal of the input bypass capacitor as close as possible to the v in pin, and the negative capacitor terminal as close as possible to the gnd pin. en/uv (pin 2/pin 4) : the LT8619 is shut down when this pin is low and active when this pin is high. the en/uv pin power-on threshold is 1v . when forced below 0.56v, the ic is put into a low current shutdown mode. tie to v in if shutdown feature is not used. an external resistor divider from v in can be used to program the v in uvlo. rt (pin 3/pin 5) : a resistor is tied between rt and ground to set the switching frequency. when synchronizing, the r t resistor should be chosen to set the LT8619 switch - ing frequency equal to or below the synchronization fre- quency. do not apply external voltage to this pin. pg (pin 4/pin 6): open-drain power good output. pg remains low until the fb pin is within 7.5% of the final regulation voltage. the pg pull-up resistor can be con - nected to the intv cc , v out or an external supply voltage that is lower than 6v. sync (pin 5/pin 7): external clock synchronization input. tie to a clock source for synchronization to an external frequency. during clock synchronization, the controller enters forced continuous mode. ground the sync pin for burst mode operation. connect to intv cc to enable forced continuous mode operation. floating this pin will enable pulse-skipping mode operation. during start-up, the con - troller is forced to run in pulse-skipping mode. when in pulse-skipping or forced continuous mode operation, the i q will be much higher compared to burst mode operation. fb (pin 6/pin 9, 10, LT8619 only): the LT8619 regulates the fb pin to 0.8v. connect the feedback resistor divider tap to this pin. also, connect a phase lead capacitor between fb and v out . typically, this capacitor is between 4.7pf to 10pf. do not apply an external voltage to this pin. out (pin 9, 10, LT8619-5 msop only): connect to the regulator output v out . the LT8619-5 regulates the out pin to 5v. this pin connects to the internal 10m feed - back divider that programs the fixed output voltage. bias (pin 7/pin 11) : the internal regulator will draw cur - rent from bias instead of v in when the bias pin is tied to a voltage higher than 3.1v . for switching regulator output voltages of 3.3v and above, this pin should be tied to v out . if this pin is tied to a supply other than v out , use a 1f local bypass capacitor on this pin. intv cc (pin 8/pin 12): internal 3.3v regulator output. the internal power drivers and control circuits are pow - ered from this voltage. intv cc maximum output current is 20ma . intv cc current will be supplied from bias if v bias > 3.1v , otherwise current will be drawn from v in . voltage on intv cc will vary between 2.8v and 3.3v when v bias is between 3.0v and 3.5v . decouple this pin to gnd with at least a 1f low esr ceramic capacitor. do not load the intv cc pin with external circuitry. bst (pin 9/pin 14): this pin is used to provide a drive voltage, higher than the input voltage, to the topside power switch. place a 0.1f boost capacitor as close as possible to the?ic. sw (pin 10/pin 15, 16): the sw pin is the output of the internal power switches. connect this pin to the inductor and boost capacitor. this node should be kept small on the pcb for good performance. gnd (exposed pad pin 11/pin 8, exposed pad pin 17) : ground. the exposed pad must be connected to the nega - tive terminal of the input capacitor and soldered to the pcb in order to lower the thermal resistance. (dfn/msop) LT8619/LT8619-5 8619f
11 for more information www.linear.com/LT8619 block diagram ? + logic r c v c i ss sw gnd fb/out 0.74v npg ? + ov ov ov 0.86v 8619 bd 0.83v pg sync rt en/uv r3 opt 1v enable v out = 5v c b c intvcc c in c out c ss c c c1 v out r1 r4 opt r t r2 l bst bias intv cc intv cc 3.3v ldo v in 0.8v v ref + ? + ea slope comp burst detect osc 0.3mhz?2.2mhz glitch filter ? + s r icmp v in v in q clk ? + ppg ? + uvlo pg LT8619/LT8619-5 8619f
12 for more information www.linear.com/LT8619 operation the LT8619 is a monolithic, constant frequency current mode step-down dc/dc converter. an oscillator, with fre - quency set using a resistor on the rt pin, turns on the internal top power switch at the beginning of each clock cycle. current in the inductor then increases until the cur - rent comparator trips and turns off the top power switch. the peak inductor current at which the top switch turns off is controlled by the voltage on the internal vc node. the error amplifier servos the vc node by comparing the volt - age on the fb pin with an internal 0.8v reference. when the load current increases, it causes a reduction in the feedback voltage relative to the reference leading the error amplifier to raise the vc voltage until the average induc - tor current matches the new load current. when the top power switch turns off, the bottom power switch turns on until the next clock cycle begins or inductor current falls to zero (burst mode operation or pulse-skipping mode). if overload conditions result in more than 1.8a flowing through the bottom switch, the next clock cycle will be delayed until the switch current returns to a safe level. if the en/uv pin is low, the LT8619 is shut down and draws less than 0.6a from the input. when the en/uv pin is above 1v, the switching regulator starts operation. first, the internal ldo powers up, followed by the switch - ing regulator 200s soft-start ramp. during the soft-start phase, the switcher operates in pulse-skipping mode and gradually switches to forced continuous mode when v out approaches the set point (if sync pin is forced high or connected to an external clock). typically, upon en/uv rising edge, it takes about 660s for the switcher output voltage to reach regulation and pg to be asserted. to optimize efficiency at light loads, configure the LT8619 to operate in burst mode by grounding the sync pin. at light load, in between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current. in a typical application, 6a will be consumed from the supply when regulating with no load. float the sync pin to enable pulse-skipping mode operation. while in pulse-skipping mode, the oscillator operates continuously and the bottom power switch turns off when the inductor current falls to zero. during light loads, switch pulses are skipped to regulate the output and the quiescent current will be higher than burst mode operation. connecting the sync pin to intv cc enables forced continuous mode operation. in forced continuous mode, the inductor current is allowed to reverse and the switcher operates at a fixed frequency. if a clock is applied to the sync pin, the part operates in forced continuous mode and synchronizes to the external clock frequency; with the rising sw signal synchronized to the external clock positive edge. to improve efficiency across all loads, supply current to internal circuitry can be sourced from the bias pin when biased above 3.1v . else, the internal circuitry will draw current from v in . the bias pin should be connected to v out if the LT8619 output is programmed to 3.3v or above. an overvoltage comparator, ov, guards against transient overshoots. if v fb is higher than 0.83v , the ov compara - tor trips, disables the top mosfet and turns on the bot - tom power switch until the next clock cycle begins or the inductor reverse current reaches 0.55a . with high reverse current, both top and bottom mosfets shut off till the next cycle. positive and negative power good compara - tors pull the pg pin low if the fb voltage varies more than 7.5% (typical) from the set point. the oscillator reduces the LT8619 s operating frequency when the voltage at the fb pin is low. this frequency foldback helps to control the inductor current when the output voltage is lower than the programmed value which occurs during overcurrent conditions. LT8619/LT8619-5 8619f
13 for more information www.linear.com/LT8619 applications information achieving ultralow quiescent current to enhance efficiency at light loads, the LT8619 enters into burst mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and output ripple voltage. in burst mode operation the LT8619 delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor. while in sleep mode the LT8619 consumes less than 6a. as the output load decreases, the frequency of single cur - rent pulses decreases (see figure?1) and the percentage of time the LT8619 is in sleep mode increases, result - ing in much higher light load efficiency than for typical converters. for a typical application, when the output is not loaded, by maximizing the time between pulses, the regulator quiescent approaches 6a. therefore, to opti - mize the quiescent current performance at light loads, the current in the feedback resistor divider must be mini - mized as it appears to the output as load current (see fb resistor network section). while in burst mode operation, the current limit of the top switch is approximately 380ma resulting in output voltage ripple shown in figure?2. increasing the output capacitance will decrease the output ripple proportionally. as load ramps upward from zero, the switching frequency will increase but only up to the switching frequency programmed by the resistor at the rt pin as shown in figure?1. the output load at which the LT8619 reaches the programmed frequency varies based on input voltage, output voltage, and inductor choice. for some applications it is desirable for the LT8619 to operate in pulse-skipping mode, offering two major dif - ferences from burst mode operation. first, the minimum inductor current clamp present in burst mode operation is removed, providing a smaller packet of charge to the output capacitor and reduce the output ripple voltage. for a given load, the chip awake more often, resulting in higher supply current compared to burst mode opera - tion. second is that full switching frequency is reached at lower output load than in burst mode operation (see figure?3). to enable pulse-skipping mode, leave the sync pin floating. tying the sync pin to intv cc node enables the programmed switching frequency at no load. figure?1. burst frequency vs load current 8619 f02 v out (ac) 10mv/div i l 200ma/div sw 10v/div sw (zoom in) 10v/div i l (zoom in) 200ma/div v out (ac, zoom in) 10mv/div top = 20ms/div, bot = 1s/div figure?2. burst mode operation waveform with v in = 12v, v out = 3.3v at no load, r t = 66.5k, l = 10h, c out = 22f figure?3. minimum load for full frequency operation vs v in in burst mode operation and pulse-skipping mode setting LT8619/LT8619-5 8619f in (v) 0 10 20 30 40 50 60 0 v 50 100 150 200 250 300 350 400 load current (ma) 8619 f03 out pulse-skipping mode burst mode operation v in = 12v v out = 3.3v f osc = 700khz l = 10h burst mode operation load current (ma) 0.001 0.01 = 3.3v 0.1 1 10 100 1k 0.01 0.1 1 10 100 f 1k f sw (khz) 8619 f01 osc = 700khz l = 10h v
14 for more information www.linear.com/LT8619 applications information fb resistor network the output voltage is programmed with a resistor divider between v out and the fb pin. choose the resistor values according to: r1 = r2 v out 0.8v C 1 ? ? ? ? ? ? reference designators refer to the block diagram. 1% resistors are recommended to maintain output voltage accuracy. if low input quiescent current and good light-load effi - ciency are desired, use a large resistor value for the fb resistor divider. the current flowing in the divider acts as a load current, and will increase the no-load input current to the converter, which is approximately: i q = 5.2a + v out r1 + r2 ? ? ? ? ? ? ? ? v out v in ? ? ? ? ? ? ? ? ? ? 1 ? ? ? ? ? ? ? ? where 5.2a is the quiescent current of the LT8619 and the second term is the current in the feedback divider reflected to the input of the buck operating at its light load efficiency, . for a 3.3v application with r1 = 1m and r2 = 316k , the feedback divider draws 2.5a from v out . with v in = 12v and = 85%, this adds 0.8a to the 5.2a quiescent current resulting in 6a quiescent current from the 12v supply. note that this equation implies that the no-load current is a function of v in ; this is plotted in the typical performance characteristics section. when using large fb resistors, a 4.7pf to 10pf phase lead capacitor, c1, should be connected from v out to fb. setting the switching frequency the LT8619 uses a constant frequency pwm architec - ture that can be programmed to switch from 300khz to 2.2mhz by using a resistor tied from the rt pin to ground. the r t resistor required for a desired oscillator frequency can be roughly obtain using: r t = 50.07 f osc C 5 where r t is in k and f osc is the desired switching fre - quency in mhz. table 1 and figure? 4 show the typical r t value for a desired oscillator frequency. table 1. oscillator frequency vs r t value (1% standard value) f osc (mhz) r t (k) f osc (mhz) r t (k) 0.3 162 1.4 30.9 0.4 121 1.6 26.1 0.5 95.3 1.8 22.6 0.6 78.7 2.0 20.0 0.7 66.5 2.2 17.8 0.8 57.6 0.9 51.1 1.0 45.3 1.2 36.5 figure?4. oscillator frequency vs r t value operating frequency selection and trade-offs selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. the advantage of high frequency operation is that smaller inductor and capacitor values may be used. the disadvan - tages are lower efficiency and a smaller input voltage range. for force continuous mode operation, the highest oscil - lator frequency (f osc(max) ) for a given application can be approximately given by the 1st order equation: f osc(max) = i load r sw(bot) + v out t on(min) v in C i load r sw(top) + i load r sw(bot) ( ) where v in is the input voltage, v out is the output volt- age, r sw(top) and r sw(bot) are the internal switch on resistance ( ~0.45?, ~0.22?, respectively) and t on(min) LT8619/LT8619-5 8619f 140 160 0.2 0.6 1.0 1.4 1.8 2.2 f osc (mhz) 8619 f04 r t (k) 0 20 40 60 80 100 120
15 for more information www.linear.com/LT8619 applications information is the minimum top switch on-time at the loading condi - tion as shown in figure?5. figure?6 shows the relation - ship between the maximum input voltage vs the switching frequency. if a smaller r t is selected, to ensure that the regulator is switching at the higher frequency as illus - trated in figure?4, the maximum input supply voltage has to be lowered; and it needs to be further reduced if the load is decreased or removed. for forced continuous mode, if there is a momentarily v in voltage surge higher than the voltage shown in figure?6, resulting in minimum on-time operation, an overvoltage comparator guards against transient overshoots as well as other more serious conditions that may overvoltage the output. when the v fb voltage rises by more than 3.75% above its nominal value, the top mosfet is turned off and the bottom mosfet is turned on. at this moment, the output voltage continues to increase until the inductor current reverses. the actual peak output voltage will be higher than 3.75%, depending on external components value, loading condition and output voltage setting. the bottom mosfet remains on continuously until the induc - tor current exceeds the bottom mosfet reverse current or overvoltage condition is cleared. with high reverse cur - rent, both top and bottom mosfets shut off till the next clock cycle. low supply operation the LT8619 is designed to remain operational during short line transients when the input voltage may briefly dip below 3.0v . below this voltage, the intv cc voltage might drop to a point that is not able to provide adequate gate drive voltage to turn on the mosfet. the LT8619 has two circuits to detect this undervoltage condition. a uvlo comparator monitors the intv cc voltage to ensure that it is above 2.8v during startup; once in regulation, the chip continues to operate as long as intv cc stays above 2.65v. if this uvlo comparator trips, the chip is shut down until intv cc recovers. another comparator monitors the v in supply voltage, add a resistor divider from v in to en/uv to turn off the regulator if v in dips below the undesirable voltage. the LT8619 is capable of a maximum duty cycle of greater than 99%, and the v in -to-v out dropout is limited by the r ds(on) of the top switch. in deep dropout, the loop attempt to turn on the top switch continuously. however, the top switch gate drive is biased from the floating boot- strap capacitor c b , which normally recharges during each off cycle; in dropout, this capacitor loses its refresh cycle and charge depleted. a comparator detects the drop in boot-strap capacitor voltage, forces the top switch off and recharges the capacitor. figure?5. minimum on-time vs load current figure?6. forced continuous mode maximum input voltage vs switching frequency high supply operation for burst mode operation or pulse-skipping mode, v in voltage may go as high as the absolute maximum rating of 60v regardless of the frequency setting ; however, the LT8619 will reduce the switching frequency as necessary to regulate the output voltage. LT8619/LT8619-5 8619f 0.6 0.8 1.0 1.2 0 10 20 30 40 50 v out = 3.3v 60 70 80 minimum on-time (ns) 8619 f05 v out = 3.3v l = 10h forced continuous mode 0.2a load f sw (mhz) f sw = 2mhz 0.2 0.6 1.0 1.4 1.8 2.2 0 10 20 30 l = 3.3h 40 50 60 maximum v in (v) 8619 f06 0.5a load no load forced continuous mode load current (a) 0 0.2 0.4
16 for more information www.linear.com/LT8619 for low v in applications that cannot allow deviation from the programmed oscillator frequency, use the following formula to set the switching frequency: v in(min) = v sw(bot) + v out 1C t off(min) ? f osc + v sw(top) C v sw(bot) where v in(min) is the minimum input voltage without skipped cycles, v out is the output voltage, v sw(top) and v sw(bot) are the internal switch drops ( ~0.54v, ~0.264v, respectively at maximum load), f osc is the oscillating fre - quency (set by r t ), and t off(min) is the minimum switch - ing off-time. note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. inductor selection and maximum output current the LT8619 is designed to minimize solution size by allowing the inductor to be chosen based on the output load requirements of the application. during overload or short-circuit conditions the LT8619 safely tolerates opera - tion with a saturated inductor through the use of a high speed peak-current mode architecture. a good first choice for the inductor value is: l = 2 v out + v sw(bot) f osc where f osc is the switching frequency in mhz, v out is the output voltage, v sw(bot) is the bottom switch drop (~0.264v) and l is the inductor value in h. to avoid overheating and poor efficiency, an inductor must be chosen with an rms current rating that is greater than the maximum expected output load of the applica - tion. in addition, the saturation current (typically labeled i sat ) rating of the inductor must be higher than the load current plus one-half of inductor ripple current: i sat > i load(max) + i l(max) 2 applications information where i load(max) is the maximum output load for a given application and ?i l(max) is the inductor ripple current as calculated in the following equation: i l(max) = 1 f osc ? l v out 1C v out v in(max) ? ? ? ? ? ? ? ? as a quick example, an application requiring 1a output current should use an inductor with an rms rating of greater than 1a and an i sat of greater than 1.5a. during long duration overload or short-circuit conditions, the inductor rms rating requirement is greater to avoid over - heating of the inductor. to push for high efficiency, select an inductor with low series resistance (dcr), preferably below 0.04? , and the core material should be intended for high frequency application. however, achieving this requires a large size inductor. an inductor with dcr around 0.1 ? is generally a good compromise for both efficiency and board area, at the expense of trimming 1% to 2% from the efficiency number. the LT8619 limits the peak switch current in order to pro - tect the switches and the system from overload faults. the top switch current limit (i lim ) is at least 1.5a. the induc- tor value must then be sufficient to supply the desired maximum output current (i load(max) ), which is a function of the switch current limit (i lim ) and the ripple current: i load(max) = i lim C i l 2 therefore, the maximum output current that the LT8619 will deliver depends on the switch current limit, the induc - tor value, and the input and output voltages. the inductor value may have to be increased if the inductor ripple cur - rent does not allow sufficient maximum output current (i load(max) ) given the switching frequency, and maximum input voltage used in the desired application. in order to achieve higher light load efficiency, more energy must be delivered to the output during single small pulses in burst mode operation such that the LT8619 can LT8619/LT8619-5 8619f
17 for more information www.linear.com/LT8619 applications information stay in sleep mode longer between each pulse. this can be achieved by using a larger value inductor, and should be considered independent of switching frequency when choosing an inductor. for example, while a lower inductor value would typically be used for a high switching fre - quency application, if high light load efficiency is desired, a higher inductor value should be chosen. the optimum inductor for a given application may differ from the one indicated by this design guide. a larger value inductor provides a higher maximum load current and reduces the output voltage ripple. for applications requir - ing smaller load currents, the value of the inductor may be lower and the LT8619 may operate with higher ripple current. this allows you to use a physically smaller induc - tor, or one with a lower dcr resulting in higher efficiency. be aware that low inductance may result in discontinuous mode operation, which further reduces maximum load current. for details of maximum output current and discontinuous operation, see analog devicess application note 44. input capacitor step-down regulators draw current from the input sup - ply in pulses with very fast rise and fall times. the input capacitor is required to reduce the resulting voltage rip - ple at the LT8619 and to force this very high frequency switching current into a tight local loop, minimizing emi. in continuous mode, the input capacitor rms current is given by : i rms(max) i load(max) v out v in C v out ( ) v in this equation has a maximum rms current at v in = 2v out , where i rms(max) = i load(max) /2. bypass the input of the LT8619 circuit with a 2.2f to 10f ceramic capacitor of x7r or x5r type placed as close as possible to the v in and gnd pin. y5v types have poor performance over temperature and applied voltage, and should not be used. note that larger input capacitance is required when a lower switching frequency is used. if the input power source has high impedance, or there is significant inductance due to long wires or cables, a ceramic input capacitor combined with the trace or cable inductance forms a high quality (underdamped) tank cir - cuit. if the LT8619 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8619s voltage rating. this situation is easily avoided (see analog devices application note?88), by adding a lossy electrolytic capacitor in parallel with the ceramic capacitor. output capacitor and output ripple the output capacitor has two essential functions. along with the inductor, it filters the square wave generated by the LT8619 to produce the dc output. in this role it determines the output ripple, thus low impedance at the switching frequency is important. the second function is to store energy in order to satisfy transient loads and stabilize the LT8619s control loop. the current slew rate of a regulator is limited by the inductor and feedback loop. when the amount of current required by the load changes, the initial current deficit must be supplied by the output capacitor until the feedback loop reacts and compensates for the load changes. ceramic capacitors have very low equivalent series resistance (esr) and provide the best ripple performance. for good starting values, see the typical applications section. transient performance can be improved with a higher value capacitor and the addition of a feedforward capaci - tor placed between v out and fb. increasing the output capacitance will also decrease the output voltage ripple. a lower value of output capacitor can be used to save space and cost but transient performance will suffer and may cause loop instability. see the typical applications in this data sheet for suggested capacitor values. ceramic capacitors when choosing a capacitor, special attention should be given to the manufacturers data sheet in order to accu - rately calculate the effective capacitance under the rel - evant bias voltage and operating temperature conditions. ceramic dielectrics can offer near ideal performance as LT8619/LT8619-5 8619f
18 for more information www.linear.com/LT8619 applications information an output capacitor, i.e. high volumetric efficiency with extremely low equivalent resistance. there is a downside however; the high k dielectric material exhibits a substan - tial temperature and voltage coefficient, meaning that its capacitance varies depending on the operating tempera - ture and applied voltage. x7r capacitors provide a range intermediate capacitance values which varies only 15% over the temperature range of C55c to 125c. the y5v capacitance can vary from 22% to C82% over the C30c to 85 c temperature range and should not be used for the LT8619 application. figure?7 shows the voltage coefficient of four different ceramic 22f capacitors, all of which are rated for 16v operation. note that with the exception of the x7r in the 1210 and 1812 package, the capacitors lose more than 30% of their capacitance when biased at more than half of the rated voltage. typically, as the package size increases, the bias voltage coefficient decreases. if the voltage coef - ficient of a big ceramic capacitor in a particular pack - age size is not acceptable; multiple smaller capacitors with less voltage coefficient can be placed in parallel as an effective means of meeting the capacitance require - ment. not all capacitors are interchangeable . a wrong capacitor selection can degrade the circuit performance considerably. ceramic capacitors can also cause problems due to their piezoelectric nature. during burst mode operation, the switching frequency depends on the load current, and at very light loads the LT8619 can excite the ceramic capaci - tor at frequencies that may generate audible noise. since the LT8619 operates at a lower inductor current during burst mode operation, the noise is typically very quiet to a casual ear. if this is unacceptable, consider using a high performance tantalum or electrolytic capacitor at the output instead. low noise ceramic capacitors are also available. ceramic capacitors are also susceptible to mechanical stress which can result in significant loss of capacitance. the most common sources of mechanical stress includes bending or flexure of the pcb, contact pressure during in circuit parameter testing, and direct contact by a solder - ing iron tip. consult the manufacturers application notes for additional information regarding ceramic capacitor handling. enable pin the LT8619 is in shutdown when the en/uv pin is low and active when the pin is high. the power-on threshold of the?en comparator is 1.0v, with 40mv of hysteresis, once en/uv drops below this power-on threshold, the mosfets are disabled, but the internal biasing circuit stays alive. when forced below 0.56v , all the internal blocks are disabled and the ic is put into a low current shutdown mode. the en/uv pin can be tied to v in if the shutdown feature is not used. adding a resistor divider from v in to en/uv programs the LT8619 to regulate the output only when v in is above a desired voltage (see the block diagram). typically, this threshold, v in(en/uv) , is used in situations where the input supply is current limited, or has a relatively high source resistance. a switching regulator draws constant power from the source, so source current increases as source voltage drops. this looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. the v in(en/uv) threshold prevents the regulator from operating at source voltages where the problems might occur. this figure?7. ceramic capacitor voltage coefficient LT8619/LT8619-5 8619f dc bias voltage (v) 0 2 4 6 8 10 12 14 16 x7r, 1210 ?100 ?80 ?60 ?40 ?20 0 20 capacitance change (%) 8619 f09 x7r, 1812 x5r, 1206 x5r, 0805 c3225x7r1c226k250 c4532x7r1c226m200 c3216x5r1c226m160 c2012x5r1c226k125
19 for more information www.linear.com/LT8619 applications information threshold can be adjusted by setting the values r3 and r4 such that they satisfy the following equation: v in(en/uv) = 1 + r3 r4 ? ? ? ? ? ? ? 1v where the LT8619 will remain off until v in is above v in(en/uv) . due to the comparators hysteresis, switching will not stop until the input falls slightly below v in(en/uv) . when in burst mode operation for light load currents, the current through the v in(en/uv) resistor network can easily be greater than the supply current consumed by the LT8619 . therefore, the v in(en/uv) resistors should be large enough to minimize their impact on efficiency at low loads. intv cc regulator an internal low dropout (ldo) regulator produces the 3.3v supply from v in that powers the drivers and the internal bias circuitry. the intv cc can supply enough current for the LT8619 s circuitry and must be bypassed to ground with at least a 1f ceramic capacitor. good bypassing is necessary to supply the high transient currents required by the power mosfet gate drivers. to improve efficiency the internal ldo can draw current from the bias pin when the bias pin is at 3.1v or higher. typically the bias pin can be tied to the output of the switching regulator, or can be tied to an external supply which must also be at 3.3v or above. if bias is connected to a supply other than v out , be sure to bypass with a local ceramic capacitor. if the bias pin is below 3.0v , the internal ldo will consume current from v in . applications with high input voltage and high switching frequency where the internal ldo pulls current from v in will increase die temperature because of the higher power dissipation across the ldo. do not connect an external load to the intv cc pin. output power good when the LT8619s output voltage is within the 7.5% window of the regulation point, the open-drain pg pin goes high impedance and is typically pulled high with an external resistor. otherwise, the internal open-drain tran - sistor will pull the pg pin low. the pg pin is also actively pulled low during several fault conditions: en/uv pin is below 1v , intv cc drops below its uvlo threshold, v in is too low, or thermal shutdown. synchronization synchronizing the LT8619 oscillator to an external fre - quency can be done by connecting a square wave (with 20% to 80% duty cycle) to the sync pin. the square wave amplitude should have valleys that are below 0.4v and peaks above 2v (up to 6v). during frequency synchroni - zation, the part operates in forced continuous mode with the sw rising edge synchronized to the sync positive edge. the LT8619 may be synchronized over a 300khz to 2.2mhz range. the r t resistor must be chosen to set the LT8619 switching frequency equal or below the lowest synchronization input. for example, if the synchroniza - tion signal will be 500khz and higher, the r t should be selected for 500khz. start-up inrush current, short-circuit protection upon start-up, the internal soft-start action regulates the v out slew rate; the LT8619 provides the maximum rated output current to charge up the output capacitor as quickly as possible. during start-up, if the output is overloaded, the regulator continues to provide the maxi- mum sourcing current to overcome the output load, but at the same time, the bottom switch current is monitored such that if the inductor current is beyond the safe levels, switching of the top switch will be delay until such time as the inductor current falls to safe levels. once the soft-start period has expired and the fb voltage is higher than 0.74v , the LT8619 switching frequency will be folded back if the external load pulls down the output. at the same time, the bottom switch current will continue to be monitored to limit the short-circuit current. figure 8 shows the frequency foldback transfer curve and figure 9 shows the short circuit waveform. during this overcurrent condition, if the sync pin is connected to a clock source, the LT8619 will get out from the synchronization mode. LT8619/LT8619-5 8619f
20 for more information www.linear.com/LT8619 figure?8. frequency foldback transfer function figure?9. short-circuit waveform with v in = 12v, v out = 3.3v, f osc = 2mhz, l = 4.7h, c out = 22f v in v in LT8619 en/uv gnd 8619 f10 pcb layout for proper operation and minimum emi, care must be taken during printed circuit board (pcb) layout. figure?11 and figure?12 show the recommended component place - ment with trace, ground plane and via locations. note that large, switched currents flow in the LT8619 s v in , sw, gnd pins, and the input capacitor. the loop formed by these components should be as small as possible by plac - ing the capacitor adjacent to the v in and gnd pins. when using a physically large input capacitor, the resulting loop may become too large in which case using a small case/ value capacitor placed close to the v in and gnd pins plus a larger capacitor further away is preferred. these com - ponents, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. place a local, unbroken ground plane under the application cir - cuit on the layer closest to the surface layer. the sw and bst nodes should be as small as possible. finally, keep the fb and rt nodes small so that the ground traces will shield them from the sw and bst nodes. the exposed pad on the bottom of the package must be soldered to ground so that the pad is connected to ground electrically and also acts as a heat sink thermally. to keep thermal resistance low, extend the ground plane as much as pos - sible, and add thermal vias under and near the LT8619 to additional ground planes within the cir cuit board and on the bottom side. high temperature output current considerations the maximum practical continuous load that the LT8619 can drive, while rated at 1.2a , actually depends upon both the internal current limit (refer to the typical performance characteristics section) and the internal temperature which depends on operating conditions, pcb layout and airflow. applications information 5s/div v out 1v/div i short 10a/div i l 0.5a/div sw 10v/div 8619 f09 reversed input protection load protection may be necessary in systems where the output will be held high when the input to the LT8619 is absent. this may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ored with the LT8619s output. if the v in pin is allowed to float and the en/uv pin is held high (either by a logic signal or because it is tied to v in ), then the LT8619 s internal circuitry will pull its quiescent current through its sw pin. this is acceptable if the system can tol - erate several a in this state. if the en/uv pin is grounded the sw pin current will drop to near 1a . however, if the v in pin is grounded while the output is held high, regard - less of en/uv, parasitic body diodes inside the LT8619 can pull current from the output through the sw pin and the v in pin. figure?10 shows a connection of the v in and en/uv pins that will allow the LT8619 to run only when the input voltage is present and that protects against a shorted or reversed input. figure?10. reverse v in protection LT8619/LT8619-5 8619f 0.6 0.7 0.8 0 0.5 1.0 1.5 2.0 2.5 f sw (mhz) r t = 20k 8619 f08 v fb (v) 0 0.1 0.2 0.3 0.4 0.5
21 for more information www.linear.com/LT8619 applications information en/uv pg sync rt gnd sw v out v in intv cc bst bias v out fb/out + 8619 f12 en/uv pg rt sync rt gnd sw v out v in bst intv cc bias v out fb/out + 8619 f11 figure?11. recommended pcb layout for LT8619 10-pin dfn figure?12. recommended pcb layout for LT8619 16-pin msop LT8619/LT8619-5 8619f
22 for more information www.linear.com/LT8619 figure?13. case temperature rise vs load current figure?14. case temperature rise vs ambient temperature for higher ambient temperatures, care should be taken in the layout of the pcb to ensure good heat sinking of the LT8619. the exposed pad on the bottom of the package must be soldered to a ground plane. this ground should be tied to large copper layers below with thermal vias ; these layers will spread heat dissipated by the LT8619. placing additional vias can reduce thermal resistance fur - ther. figure?13 shows the rise in case temperature vs load current. note that a higher ambient temperature will result in bigger case temperature rise as shown in figure?14. power dissipation within the LT8619 can be estimated by calculating the total power loss from an efficiency measurement and subtracting the inductor loss. the die temperature is calculated by multiplying the LT8619 power dissipation by the thermal resistance from junction to ambient. figure?15 shows the typical derating maximum output current curve. as with any monolithic switching regu - lator, the pcb layout, thermal resistance, air flow, other heat sources in the vicinity affect how efficiently heat can be removed from the die and radically change the die junction temperature. the actual LT8619 switcher output voltage and current sourcing capability might deviate from the performance curve stated in this data sheet. when pushing the LT8619 to its limit, verify its operation in the actual environment. at high ambient temperature, continuous operation above the maximum operation junction temperature may impair device reliability or permanently damage the device. figure?15. LT8619 derating maximum output current with junction temperature less than 125c applications information LT8619/LT8619-5 8619f 0.4 0.6 0.8 1.0 1.2 0 5 10 15 20 v in = 12v case temperature rise (c) 8619 f13 v in = 12v v out = 5v, 1.2a load f sw = 700khz continuous operation above maximum junction temperature may permanently damage the device ambient temperature (c) 25 v out = 5v 50 75 100 125 0 5 10 15 20 25 f sw = 700khz 30 35 case temperature rise (c) 8619 f14 v in = 12v v out = 3.3v t j(max) 125c forced continuous mode ambient temperature (c) 90 t a = 25c 95 100 105 110 115 120 125 0 0.2 0.4 forced continuous mode 0.6 0.8 1.0 1.2 1.4 maximum output current (a) 8619 f15 f sw = 700khz f sw = 2mhz load current (a) 0 0.2
23 for more information www.linear.com/LT8619 3.3v 400khz step-down converter typical applications 15h pg 100k 1m 316k 121k 0.1f 22f 8619 ta02 v out 3.3v 1.2a bst sw pg bias fb gnd sync rt 6.8pf l = vishay ihlp-3232cz-11 c out = tdk c3225x7r1c226k250 f osc = 400khz off on 1f 2.2f v in 4v to 60v intv cc v in en/uv LT8619 1.8v 2mhz step-down converter LT8619 2.2h pg pg 100k 1.87m 1.5m 20k off on 0.1f 22f 5.6pf 8619 ta03 1f 2.2f v in 3.3v to 12v v out 1.8v 1.2a bst sw intv cc v in gnd sync en/uv rt l = vishay ihlp-2020ab-01 c out = tdk c3225x7r1c226k250 fb bias f osc = 2mhz 5v 2mhz step-down converter 12v 700khz step-down converter LT8619-5 4.7h 20k 0.1f 22f 8619 ta04 v in 6v to 36v (60v transient) v out 5v 1.2a bst sw gnd sync rt bias out off on 1f 2.2f intv cc v in en/uv pg pg 100k l = vishay ihlp-2020bz-01 c out = tdk c3225x7r1c226k250 f osc = 2mhz LT8619 22h pg pg 100k 0.931m 401k 66.5k 66.5k off on 0.1f 10f 2 22pf 8619 ta05 1f 2.2f v in 13v to 60v v out 12v 1.2a bst sw intv cc v in gnd sync en/uv rt fb bias l = vishay ihlp-2020cz-11 c out = murata grm32er7ya106k f osc = 700khz LT8619/LT8619-5 8619f
24 for more information www.linear.com/LT8619 package description please refer to http://www.linear.com/product/LT8619#packaging for the most recent package drawings. dd package 10-lead plastic dfn (3mm 3mm) (reference ltc dwg # 05-08-1699 rev c) 3.00 0.10 (4 sides) note: 1. drawing to be made a jedec package outline m0-229 variation of (weed-2). check the ltc website data sheet for current status of variation assignment 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 0.10 bottom view?exposed pad 1.65 0.10 (2 sides) 0.75 0.05 r = 0.125 typ 2.38 0.10 (2 sides) 1 5 10 6 pin 1 top mark (see note 6) 0.200 ref 0.00 ? 0.05 (dd) dfn rev c 0310 0.25 0.05 2.38 0.05 (2 sides) recommended solder pad pitch and dimensions 1.65 0.05 (2 sides) 2.15 0.05 0.50 bsc 0.70 0.05 3.55 0.05 package outline 0.25 0.05 0.50 bsc dd package 10-lead plastic dfn (3mm 3mm) (reference ltc dwg # 05-08-1699 rev c) pin 1 notch r = 0.20 or 0.35 45 chamfer LT8619/LT8619-5 8619f
25 for more information www.linear.com/LT8619 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. package description msop (mse16) 0213 rev f 0.53 0.152 (.021 .006) seating plane 0.18 (.007) 1.10 (.043) max 0.17 ?0.27 (.007 ? .011) typ 0.86 (.034) ref 0.50 (.0197) bsc 16 16151413121110 1 2 3 4 5 6 7 8 9 9 1 8 note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 6. exposed pad dimension does include mold flash. mold flash on e-pad shall not exceed 0.254mm (.010") per side. 0.254 (.010) 0 ? 6 typ detail ?a? detail ?a? gauge plane 5.10 (.201) min 3.20 ? 3.45 (.126 ? .136) 0.889 0.127 (.035 .005) recommended solder pad layout 0.305 0.038 (.0120 .0015) typ 0.50 (.0197) bsc bottom view of exposed pad option 2.845 0.102 (.112 .004) 2.845 0.102 (.112 .004) 4.039 0.102 (.159 .004) (note 3) 1.651 0.102 (.065 .004) 1.651 0.102 (.065 .004) 0.1016 0.0508 (.004 .002) 3.00 0.102 (.118 .004) (note 4) 0.280 0.076 (.011 .003) ref 4.90 0.152 (.193 .006) detail ?b? detail ?b? corner tail is part of the leadframe feature. for reference only no measurement purpose 0.12 ref 0.35 ref mse package 16-lead plastic msop, exposed die pad (reference ltc dwg # 05-08-1667 rev f) please refer to http://www.linear.com/product/LT8619#packaging for the most recent package drawings. mse package 16-lead plastic msop, exposed die pad (reference ltc dwg # 05-08-1667 rev f) LT8619/LT8619-5 8619f
26 for more information www.linear.com/LT8619 lt 0118 ? printed in usa www.linear.com/LT8619 ? analog devices, inc. 2018 related parts typical application part description comments lt8602 42v, quad output (2.5a + 1.5a + 1.5a + 1.5a) 95% efficiency, 2.2mhz synchronous micropower step-down dc/dc converter with i q = 25a v in(min) = 3v, v in(max) = 42v, v out(min) = 0.8v, i q = 2.5a, i sd ?LT8619-5 4.7h l in 4.7h fb1 bead 20k 0.1f 22f 8619 ta06 4.7f v in 6v to 36v (60v transient) v out 5v 1.2a bst sw pg bias out gnd sync rt 4.7f 4.7f pg 100k off on 1f intv cc v in en/uv fb1 = tdk mpz2012s221a l in = xfl4020 l = vishay ihlp-2020bz-01 c out = tdk c3225x7r1c226k250 f osc = 2mhz LT8619/LT8619-5 8619f

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